The primary purpose of this research project is to determine the prevalence of infection by Actinobacillus actinomycetemcomitans (Aa) and Porphyromonas gingivalis (Pg) in the general population. This study will use data from the Third National Health and Nutrition Examination Survey (NHANES III) to describe the epidemiology of exposure to Aa and Pg in a large representative sample of the U.S. population (ages 12 and older). Antibody levels will then be correlated with questionnaire (sociodemographic characteristics) and examination (clinical periodontal status) data from NHANES III. The results of this study are likely to be the most systematic and comprehensive evaluation of the prevalence of the two major periodontal pathogens in the U.S. population. A contract has been let to an external laboratory to conduct the ELISA antibody tests on the 10,000 serum samples collected during Phase II of NHANES III. This testing, which has just begun, will use a monoclonal antibody detection system and a national standard reference serum pool (characterized and calibrated so that it can be used by the external community in future research).